Atlantic Cod Gadus Morhua Research Articles

Mortality, movement, and body size: critical scales for Atlantic cod (Gadus morhua) in the Northwest Atlantic

The problem of scaling spatially and temporally limited data to larger scale questions can no longer be ignored as evidence accumulates that the importance of any given process, relative to another, depends on spatial and temporal scale. A recently developed graphical technique allows identification of critical space and time scales, which separate scales at which one rate prevails from scales at which another rate prevails. We used data from the literature to test a series of hypotheses concerning change in critical scales with change with life history stage in Atlantic cod (Gadus morhua). The critical scales for mortality relative to kinematics increased slightly for pelagic juveniles relative to drifting eggs, decreased substantially for demersal juveniles relative to pelagic juveniles, increased again in adults, and, contrary to expectation, remained high in large adults ("mother fish"). Critical time and space scales were found to be linked and cannot be taken as constants.

Swimming Performance and Growth Rates of Juvenile Atlantic Cod Intraperitoneally Implanted with Dummy Acoustic Transmitters

Short-term and long-term effects of intraperitoneal implantation of dummy acoustic transmitters (1.9–4.6% of the fishes' body weight) in wild juvenile Atlantic cod Gadus morhua were investigated. Short-term effects were examined by comparing critical swimming speeds 24 h after surgery for implanted, sham-implanted, and control groups using a Blazka-style swim tube. Additionally, comparative growth rates, mortality, and tag expulsion by cod in the same three groups were determined during a 220-d period. Critical swimming speed performance between treatments was found to be nonsignificant between groups, suggesting that tagged juvenile cod are capable of similar physical performance to that of untagged cod when released 24 h after surgery. During the long-term study, no significant difference in growth between groups, no increase in mortality associated with the tagging procedure, and no incidents of transmitter expulsion occurred. This study suggests that intraperitoneal implantation of acoustic transmitters can be a valid tagging technique to examine the behavior of juvenile Atlantic cod in both short-term and long-term studies.

Growth, condition, and environmental relationships in Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence and implications for management strategies in the Northwest Atlantic

Northern Gulf of St. Lawrence Atlantic cod (Gadus morhua) is one of several stocks that collapsed in eastern Canada following a long period of intensive exploitation. Surplus and net production per capita became nil or negative in the mid-1980s so that any level of exploitation would have caused a decline of the stock. This was partly explained by a marked decline in growth production and is consistent with smaller sizes-at-age but also lower condition factor values during the same period. Correlations between size-at-age and temperature were not significant when corrected for autocorrelation, but slopes were always positive, suggesting higher growth rates at higher temperatures. Smaller sizes-at-age in the 1980s were not associated with changes in the fishery or increased fishing mortality, nor were they consistent with the density-dependence hypothesis. Lengths at age 8 decreased by more than 10 cm as the stock decreased 10-fold in abundance. While size-at-age and temperature covary in cod when all stocks are examined, size-temperature relationships are not as clear if the analysis is restricted to cold-water stocks, possibly because of differences in food availability. Biological production varies from year to year and among stocks and should be taken into consideration when managing fisheries in variable or extreme environments.

Effects of release parameters on recovery rates of tagged groundfish species

A compilation of groundfish mark-recapture studies conducted in the Northwest Atlantic from 1953 to 1985 was examined by analysis of deviance to determine the effects of release parameters on subsequent recoveries of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), pollock (Pollachius virens), and American plaice (Hippoglossoides platessoides). Fish length was a major determinant of recoveries for all four species, with recovery rates generally increasing with increasing fish length. Depth of capture was a significant determinant of recoveries for cod and haddock, with recovery rates decreasing as depth increased. Year of release was a significant determinant for all four species, with recovery rates declining in recent years. Declines in recovery rates of cod, haddock, and pollock occurred during certain months or seasons. Recovery rates decreased where fish were tagged in areas most distant from inhabited coastal regions, but the interpretation of this effect is complicated by changes in the fisheries over time between areas. Recovery rates also decreased with increasing catch size and varied between different tag types and capture methods. The results should prove useful in the design of tagging protocols and analysis of recovery data.

Reduced growth of Atlantic cod in non‐lethal hypoxic conditions

Growth in length and mass, improvements in condition, as well as final condition of c. 700 g Atlantic cod Gadus morhua were significantly less at 45% and 56% O2 saturation than at 65%, 75%, 84% and 93% O2 saturation. Hypoxia decreased food consumption. In turn, food consumption explained 97% of the variation in growth. Conversion efficiency varied slightly, but significantly, with level of dissolved O2, except that the group reared at 93% O2 had a lower than expected conversion efficiency. Slow growth in low O2 was not due to increased activity, because activity decreased in hypoxia. In the Gulf of St Lawrence, waters deeper than 200 m usually are <65% saturated in O2, and thus should impact negatively on cod growth.

Gillnet selectivity for North Sea Atlantic cod (Gadus morhua): model ambiguity and data quality are related

Gillnet selectivity curves for North Sea Atlantic cod (Gadus morhua) were fitted to catch data obtained with six different mesh sizes. The selectivity curves investigated included frequently used selectivity models following the normal, lognormal, and gamma distributions. Another group of selectivity models that take the method of capture (gilled, maxillae, or "randomly" enmeshed) into consideration was also included. The best description of the selection data was found for the latter models. Therefore, the capture processes and girth measurements should be recorded as a matter of routine and such data used when constructing and evaluating gillnet selectivity models. The shape of the selectivity curve for those size intervals where there were satisfactory catch information was well defined, while the selection curve was ambiguous outside the interval with adequate data. Ambiguities in the shape of the selectivity curve can be diminished by choosing an appropriate range in mesh sizes and ensuring that the mesh sizes match the size distribution of the population fished. It is furthermore suggested that the estimated length distribution of the fish encountering the nets be robust to misspecification of the selectivity model.

The importance of detectability to acoustic surveys of semi-demersal fish

A major source of bias and imprecision in acoustic abundance estimates of semi-demersal fish is detectability, defined here as the proportion of the true abundance of a target species within the ensonified volume (surface to bottom) that is detected by an echosounder and included in integration. In autumn 1996 and 1997, acoustic surveys for Atlantic cod (Gadus morhua L.) in inshore Placentia Bay, Newfoundland, Canada, indicated mean daytime densities (e.g. 0.016 fish m −2 in 1997) an order of magnitude higher than at night (0.001 fish m −2 ). A corresponding downward shift in vertical distribution at night was also observed. At the same site in 1996,in situ video censuses of cod from a submersible showed equivalent cod abundance by day (n=3) and night (n=1). Submersible observations indicated that at night cod were located nearer to bottom, and preferred rocky and boulder-strewn substrates and not open sandy bottoms (p<0.001). Acoustic densities measured from the submersible cruising 20m above bottom, and from the surface vessel, were similar. Submersible acoustic estimates and video census indices were positively associated during daytime. The sole night-time acoustic estimate was near zero while the corresponding video index was the highest recorded. We conclude that diel change in acoustic density resulted from variations in detectability caused by cod vertical movements and habitat preferences. A broad-scale springtime inshore and offshore survey of cod in the same stock area confirmed the trend of higher acoustic density estimates during the day than at night. We advocate the inclusion of a time-dependent detectability coefficient in the scaling of acoustic backscatter to abundance for semi-demersal fish.

In vitrohydroxylation of vitamin D3and 25‐hydroxy vitamin D3in tissues of Atlantic salmonSalmo salar, Atlantic mackerelScomber scombrus, Atlantic halibutHippoglossus hippoglossusand Atlantic codGadus morhua

The in vitro metabolism of 14CD3 and 3H25OHD3 was investigated in different tissues from Atlantic salmon Salmo salar, Atlantic mackerel Scomber scombrus, Atlantic halibut Hippoglossus hippoglossus and Atlantic cod Gadus morhua. The tissues analysed were liver, kidney, head kidney, gills, spleen and intestine. The metabolites were extracted in methanol–chloroform and separated by normal-phase high-pressure liquid chromatography (HPLC) followed by scintillation counting. Identification of the metabolites was by comigration with standards on normal and reversed-phase HPLC systems and by protein-binding assays. All tissues from all species analysed produced hydroxylated derivatives identified as 25OHD3, 24,25(OH)2D3 and 1,25(OH)2D3. In addition, some unidentified derivatives were recorded, one probably being 25,26(OH)2D3. Organs producing great amounts of one metabolite also produced considerable amounts of the other possible derivatives, suggesting a lower degree of specificity in fish organs than in human organs. The predominating metabolite was 24,25(OH)2D3 in all organs from salmon and mackerel during incubation with 14CD3 and within most organs from all species during 3H25OHD3 incubation. The latter observation probably results from the need for decreasing rather than increasing the calcium absorption in these species, which live at least some periods of life in a marine environment.

Habitat-mediated survivorship of juvenile (0-year) Atlantic cod Gadus morhua

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 180:247-255 (1999) - doi:10.3354/meps180247 Habitat-mediated survivorship of juvenile (0-year) Atlantic cod Gadus morhua James B. Lindholm1,*, Peter J. Auster1, Les S. Kaufman2 1National Undersea Research Center for the North Atlantic & Great Lakes, University of Connecticut at Avery Point, Groton, Connecticut 06340, USA 2Boston University Marine Program, Boston University, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA *Present address: National Undersea Research Center for the North Atlantic & Great Lakes, University of Connecticut at Avery Point, 1084 Shennecossett Road, Groton, Connecticut 06340, USA. E-mail: lindholm@uconnvm.uconn.edu ABSTRACT: Fishing activity can impact fish populations in 2 ways. The first is the immediate effect on population demographics by the removal of fish. Second is the impact of fishing (e.g. bottom trawls and dredges) on the seafloor which can reduce habitat structure and thus increase the vulnerability of juvenile fish to predation by older conspecifics and other predators. We conducted laboratory experiments to investigate the role of variability in seafloor habitat structure on the survivorship of post-settlement juvenile (0-yr) Atlantic cod Gadus morhua. Groups of 0-yr cod were exposed to a foraging predator (3+ cod) over 5 seafloor habitats of varying complexity (sand, cobble, minimum density short sponge, maximum density short sponge, and tall sponge). These habitats were selected to mimic the range of impacts of mobile fishing gear given a gradient in fishing effort. Emergent epifauna resulted in a significant decrease in 0-yr mortality when compared to flat sand, the least complex habitat. Epifaunal density was shown to be more significant than epifaunal height in reducing 0-yr mortality. Predator reaction distance decreased with increasing habitat complexity, presumably due to the obstruction of visual cues by complex relief. Latency to first and second capture did not differ statistically between habitats. Alteration of seafloor habitat by fishing activity in the northwest Atlantic could magnify the effects of overfishing by limiting juvenile survivorship. KEY WORDS: Seafloor habitat · 0-year cod · Mortality · Survivorship · Predation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 180. Publication date: May 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Temporal changes in tissue metabolic capacities of wild Atlantic cod Gadus morhua (L.), from Newfoundland

We used biochemical indicators to assess the physiological status of Atlantic cod (Gadus morhua) sampled at different sites and times along the Newfoundland coast. The physiological status of cod changed more with time of sampling and size of the cod than with the site of sampling. The levels of muscle glycolytic enzymes and proteins suggest that cod from both near shore and offshore environments experienced the most favorable conditions in late summer and early fall. In small cod sampled near shore, increases in muscle aerobic capacity and protein contents accompanied the decrease in temperature from September to December. The positive allometry of muscle glycolytic capacities was more apparent in samples obtained in early winter than at other times, suggesting that the energetic status of cod affects the expression of this allometric relationship. On the other hand, a negative allometry of muscle aerobic capacities was apparent throughout the study. Reproductive maturity had few effects upon the biochemical parameters measured and tended to favor mature over immature cod. Our results suggest that cod in these areas were only growing in fall.

Larval Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) growth on Georges Bank: a model with temperature, prey size, and turbulence forcing

Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) on Georges Bank are subjected to a high degree of variability in temperature, turbulence, and prey densities, depending on when they are spawned and where they are advected. We have developed an individual-based model that includes the effect of varying prey density, turbulence, and temperature. Temperature effects were included by using a Q10-type adjustment to the standard metabolic rate as well as a second temperature-dependent term added to the overall ingestion ability of our model fish, a function of the swimming speed, capture efficiency, and "liveliness" of a fish. Three cases were analyzed: (i) constant food and temperature conditions, (ii) variable temperature cycles, and (iii) variable temperature cycles plus turbulence. We found that prey density, turbulence, and temperature ranges typical of the peak spawning season are variable enough to be limiting to larval growth. The timing and location of spawning are crucial to the survival of the larvae. Increasing the average temperature cycle by 1°C, as might occur due to climatological change or interannual variability, increased growth for larvae that were not growing well previously. The increased temperature failed to increase larval growth in areas where larvae were already growing at rates close to their maximum.

Seasonal variation in the habitat associations of Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) from the southern Gulf of St. Lawrence

We compared habitat associations of southern Gulf of St. Lawrence Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) between the summer feeding season on the Magdalen Shallows and the overwintering period in the Cabot Strait. Data were from bottom trawl surveys conducted in September 1993, 1994, and 1995 and January 1994, 1995, and 1996. Both species occupied much deeper, warmer water in winter than in summer. The effect of cod age on temperature distribution reversed between the two seasons, with younger cod occupying warmer water than older cod in summer and colder water in winter. Selection of both depth and temperature by cod tended to be more significant in September than in January. The reduced statistical significance of habitat selection by cod in winter was associated with a more aggregated distribution in this season. The contrast between seasons in habitat associations was particularly strong for plaice. The median habitats occupied by plaice were 58-67 m and -0.1 to 0.3°C in September and 374-426 m and 5.2-5.4°C in January. Habitat selection by plaice was significant in both seasons, but significance tended to be greater in January. Degree of aggregation in plaice distribution was similar between the two seasons. Female plaice occupied significantly warmer water than males in September but not in January. The ecological and practical implications of this striking seasonal variation in habitat associations are discussed.

Rostral-caudal variation in troponin T and parvalbumin correlates with differences in relaxation rates of cod axial muscle.

Relaxation rate is an important determinant of axial muscle power production during the oscillatory contractions of undulatory locomotion. Recently, significant differences have been reported in the relaxation rates of rostral versus caudal white muscle fibers of the Atlantic cod Gadus morhua L. The present study investigates the biochemical correlates of this rostral-caudal physiological variation. Using denaturing gel electrophoresis, a series of fresh muscle samples from the dorsal epaxial muscle region was analyzed and several differences were detected. First, a gradual shift occurs in the expression of two troponin T isoforms along the length of the body. Second, rostral muscles were found to contain significantly greater amounts of parvalbumin than caudal muscles. Third, two soluble Ca(2+)-binding proteins, in addition to parvalbumin, were also detected in the rostral muscle samples yet were absent from the caudal samples. This suite of rostral-caudal variations provides a strong biochemical basis for regional differences in the relaxation rates of cod white muscle.

Determination of extractable organic bromine and chlorine in biological compartments of Atlantic cod (Gadus morhua) by neutron activation analysis

Tissues, eggs and bile of adult Atlantic cod raised in captivity and fed natural food with no additional halogenated compounds of any kind were analyzed by neutron activation. There was a large difference in the tissue distributions of extractable organic chlorine (EOCl) and bromine (EOBr). Liver lipid had the lowest levels of EOBr and EOCl, of all the components investigated, and eggs had the highest levels of EOCl. Heart contained the most EOBr and EOCl per unit lipid, of the tissues. The presence of a larger proportion of EOBr than EOCl in bile suggests a higher rate of excretion of EOBr. The EOCl concentratios found in cod egg lipids were about 5 times higher than the highest values previously reported for EOCl in lipid.

Ca2+ uptake through voltage-gated L-type Ca2+ channels by polarized enterocytes from Atlantic cod Gadus morhua.

The presence and localization of voltage-gated Ca2+ channels of L-type were investigated in intestinal cells of the Atlantic cod. Enterocytes were loaded with the fluorescent Ca2+ probe, fure-2/AM and changes in intracellular Ca2+ concentrations ([Ca2+]i) were measured, in cell suspensions, in the presence of high potassium levels (100 mm), BAY K-8644 (5 microM), nifedipine (5 microM) or omega-conotoxin (1 microM). L-type Ca2+ channels were visualized on intestinal sections using the fluorescent dihydropyridine (-)-STBodipy. Depolarization of the plasma membrane produced a rapid (within 5 sec) and transient (at basal levels after 21 sec) increase in [Ca2+]i. BAY K-8644 increased the [Ca2+]i by 7.2%. Cells in a Ca2+-free buffer increased [Ca2+]i after addition of 10 mm Ca2+, and this increase was abolished by nifedipine in both depolarizing and normal medium but not by omega-conotoxin. Single cell experiments using video microscopy revealed that enterocytes remained polarized several hours after preparation and that the Ca2+ entry and extrusion occurred at specific and different regions of the enterocyte outer membrane. Fluorescent staining of L-type Ca2+ channels in the intestinal mucosa showed the most intense staining at the brushborder membrane. These results demonstrate the presence of voltage gated L-type Ca2+ channels in enterocytes from the Atlantic cod. The channels are mainly located at the apical side of the cells, and there is a polarized uptake of Ca2+ into the enterocytes. This suggests that the L-type Ca2+ channels are involved in the transcellular Ca2+ entry into the enterocytes.

DNA Heterozygosity and Growth Rate in the Atlantic Cod Gadus morhua (L)

DNA Heterozygosity and Growth Rate in the Atlantic Cod Gadus morhua (L)

Gear-independent patterns of variation in catch of juvenile Atlantic cod (Gadus morhua) in coastal habitats

Habitat and size of juvenile Atlantic cod (Gadus morhua) change substantially during the first 3 years after settlement, and hence, cohort size cannot be followed using a single gear. We investigated whether catch could be calibrated across gear types by deploying pairs of gears repeatedly in the same habitat. As expected, size selectivity differed substantially among gears. Trawls and seines generally collected individuals &lt;200 mm. Gillnets and jiggers collected individuals &gt;150 mm. Size modes, corresponding to age-classes, were common to catches of most gears. Highest catches were taken by trawls and seines. Gillnet catches were orders of magnitude lower. Standardized catches could not be calibrated across pairs of gears deployed in the same habitat at approximately the same time. However, it was possible to identify spatial depth gradients and diel changes in catch that were independent of gear. Consistent spatial and temporal patterns across gears were interpreted as characteristic of fish populations, not just of gears. Density in coastal habitats was higher at night and was higher at 4-7 m than at greater depths. These results, in conjunction with other studies, establish that coastal depths of 4-7 m represent the centre, and not the edge, of the distribution of age 0 cod in Newfoundland during autumn. Hence nursery areas during the early 1990s, a time of historically low spawning stock biomass, must be identified as the coastal zone, not offshore.

Sensitivity of acoustic scattering models to fish morphometry

Current efforst to model fish backscatter (e.g., Kirchoff ray-mode model [C. S. Clay and J. K. Horne, J. Acoust. Soc. Am. 96, 1661–1668 (1994)] use digitized images of fish anatomy for a more realistic representation of swimbladder shape, volume, and aspect. However, the degree of image resolution necessary for acoustic characterization and improved predictions, and the variability associated with resolution has not been quantified. Does a more accurate and higher resolution image result in improved correlation between theory and empirical measurements? Backscatter amplitudes display strong relationships with carrier frequency, swimbladder shape, and swimbladder aspect at rather high frequencies. Are predictions of these relationships influenced by image resolution? X-ray images of Atlantic cod (Gadus morhua) and brook trout (Salvelinus fontinalis) were digitized at fine resolution, and sensitivity analyses were performed to quantify the effect of varying image resolution on predicted backscatter as a function of carrier frequency and swimbladder shape and aspect. Quantifying image resolution is a step towards determining morphometric effects on backscatter variability and estimating fish abundance using multi-frequency data and the inverse approach. [Work supported by ONR.]

Egg Size and Viability and Seasonal Offspring Production of Young Atlantic Cod

Abstract Experiments monitoring the egg and larval production of captive northwest Atlantic cod Gadus morhua indicated that first-time spawners perform poorly compared to second-time spawners. They breed for a shorter period, produce fewer egg batches, exhibit lower fecundity, and produce smaller eggs with lower fertilization and hatching rates; moreover, their larvae are less likely to hatch in environmental conditions favorable for survival. Batch-average egg diameters of first-time spawners underwent a continuous rapid decline between initial and terminal batches, whereas second-time spawners commonly exhibited a parabolic curve (slight increase followed by a decrease). Seasonal composite hatching rates of all eggs spawned by first- and second-time spawners were 13 and 62%, respectively. Larval production per maternal gram was an order of magnitude greater for second-time than for first-time spawners (200 versus 20 larvae/g). Batch-average egg diameter declined 11% and larval dry weight declined 29% fr...

Nucleic acids and enzymes in Atlantic cod (Gadus morhua) differing in condition and growth rate trajectories

Atlantic cod (Gadus morhua) were exposed to one of four feeding regimes, 16 weeks of food deprivation (U) or satiation feeding (F) or two 8-week periods of food deprivation followed by satiation feeding (UF) or vice versa (FU), to determine whether relationships between nucleic acids or enzymes and growth rates result from a general enhancement of individual condition or are a direct result of enhanced growth rates. Final condition factor (K) differed between treatments, but did not differ between the mixed treatments after either 8 weeks of negative growth (FU) or 8 weeks of positive growth (UF). Intestinal cytochrome c oxidase activity matched the expected short-term growth rates, not only in fed and unfed fish but also in cod exposed to the mixed treatments (FU and UF). White muscle lactate dehydrogenase activity reflected growth rates, but initial levels were not reached within 8 weeks in FU cod. The liver glutamate pyruvate transaminase : DNA ratio reflected differences in K, but not differences in recent growth rates. Myofibrillar proteins decreased in unfed cod, while sarcoplasmic proteins followed changes in K more closely. The RNA:DNA ratio in white muscle did not reflect changes in K or changes in growth rates.